Life cycle assessment (LCA) looks at the environmental impacts of a building material over the entire life of the material, from extraction to disposal. LCA attempts to quantify these impacts for the purpose of comparing materials or buildings.
What is measured?
LCA is a scientific study of the environmental inputs and outputs to a building material, product, or a whole building throughout its life. Several environmental effects are studied in each assessment, including:
- Use of fossil fuels
- Use of non-renewable resources
- Water use
- Global warming potential
- Stratospheric ozone depletion
- Ground level ozone (smog) creation
- Effect on water bodies and organisms
- Acidification and acid deposition
- Toxic releases to air, water and land
Some of these effects cannot be exactly quantified for a specific unit of material, so estimates are used. The importance of LCA is not necessarily in the quantification of specific environmental effects, but in the comparison of products and assemblies.
Stages of Life
The life of a building material can be broken down into five phases:
- Resource extraction
- Product manufacturing
- Building occupancy and maintenance/Product use
- Building demolition/deconstruction/materials end-of-life disposition (disposal or transfer for recycling or reuse)
Extraction – The harvesting or extraction of raw materials begins the life of most building materials. Energy use, resource depletion, and carbon emissions are common effects of extraction. Replanting or reforestation efforts would be included when assessing the effects of extraction.
Manufacturing – This is where raw materials are formed into the final building product, and where most of the embodied energy and emissions are expended during a product’s life cycle.
Installation – This stage starts when the material leaves the factory, and includes transportation to the job site, to the specific installation site (i.e. transport to the roof with a crane), and the installation of the product. This important stage is often missed in many life cycle assessments.
Occupancy – A product’s useful life is assessed over the life of the entire building, including the occurrence of remodel and renovation projects. Several studies have quantified the average life of different building components, allowing for direct comparison of similar products.
Disposal – The options for a building product at the end of its useful life include disposal, reuse, or recycling. It can be difficult to anticipate what the options will be for a product by the time it reaches this phase, so it is assumed that they are the same as at the time of manufacturing.
As stated above, it is important to recognize that LCA is not an exact science and that environmental effects cannot be accurately calculated for a finite quantity of a building material. The usefulness comes with the ability to compare one product or assembly to another.
Life cycle assessment is part of the information that is available from an environmental product declaration (EPD). EPDs are becoming more prevalent and are gaining attention with their inclusion in green building certification programs such as LEED v4 and Green Globes.